Metallurgical-furnace roof



Dec. 18 1923. 1,477,811

C. J. CRAWFORD METALLURGIGAL FURNAGE ROOF Filed Aug. 14. 1923 v I I 6 -Pate'nted Dec. 1,8, 1923. v

nutren srrs CHARLES JAMES CRAWFRD, OF ST. LOUIS, MISSOURL METALLURGICAL-FURNACE ROOF.

Application le August 14, 1923. Serial No. 657,461.

To all whom it 'may concern:

Be it known that I, CHARLES J Aims CRAW- rom), a citizen of the United States, residing at St. Louis, and State of Missouri, have invented certain new and useful Improvements in Metallurgical-I1`111'nace Roofs, of

which the following is a specification, ref.

from will probably be best understood if we have a clear understanding of the silica brick of commerce, its properties and its many peculiar characteristics, ,inctludingi certain of its fundamental weaknesses.

The chemical analysis of a silica brick shows that it usuallycontains (Si02) about ninety-six per cent, (96%) bonded with two per cent (2%) milk of lime Ca (OH)2 with impurities present, such as alumina (A1203) -and iron (Fe2O of approximately one per cent (1%), each, with such variations 1n .l these figures as will admit very small quantitie's ofmagnesa and alkalies, (potash and soda).

The milk of lime bon-d, which is added in the process of manufacture` serves as the bonding agent, by which the uuburned brick is held to its moulded form, and in the process of burnin it acts as a flux promoting the formatlon of a small amount of quartz glass' which serves as a matrix for the silica or quartz crystals. In the process of burningA a silica brick, 'a series4 of inversions'take' place in which the quartz crystals begin'the process of changing to the allotropic forms cristobalite and tridymite.i These inversions or molecular con-- versions are the cause of Vexpansion 'in a silica brick. The actual bond in asilica brick is due to this expansion in whichl the crystals interlock and are firmly held together as`-long as expansion continues.

lWhen tridymite is completely formed, the limit of expansion has been reached and expansionhas ended. The force of the interlocking crystals is then spent. The brick having no other bond then loses its strength.

Silica is the strongest of all known re Afractory materials when under high heat.

lt softens perceptibly at about a red heat,

and from that point until fusion it is of good constant strength, slowly decreasing after long heating as tridymite slowly develops.

Silica brick are prone tol spall a d and are more sensitive to thesg/conditions at lower than at higher temperatures. They are equally sensitive at sudden changes otitemperatures, when under heat. They are at their best when working at constant temperature. Y

It will thus be seen that a silica brick under heat, is undergoino` within itself a 4strain or tension inits mdlecular 'or atomic parts, vin addition to the load or structural strain imposed upon it as a unit of the furnace structure of which the brick itself iS an integral part.

Thus, a silica brick in the roof of'an open hearth steel `furnace has one end exposed tothe air and the other end to a heatl of approximately three thousand degrecs F.

It is an integral art 'of an arch, the intrados end of the rick being exposed to high heat and consequently expanding more than the extrados end of the arch brick maY which Vare exposed to air. This imposs a 'great and unna-tural structural strain upon the'brick in addition to the atomic and mo lecular strains workin within each brick of the arch structure. t is the great torsion or pressure of these complicated strains that causes spalling and cracking and ultimate .failure of the arch roof. The average lifeof an open hearth steel furnace is from two to three hundredheats and covers a period of sixty to ninety days.

It is the purposeV of, this invention, in the design of brick, block or shapes for an open hearth steel furnace roof, to provide that part of the brick exposed to the greatest heat free and unrestricted opportunity to expand Without imposing upon it any of the structural strain or arch pressure. At the same time the part of the brick thus permitted to expand, affords7 to a -very great extent, a protection against the heat to that portion of the brick employed in sustaining the structural load, giving this portion of the brick that sustains the arch load, a more e'ven tempera-ture and a re- By this invention have applied to thc roof a checker effect in which l have multiplied about fourtimes the exposed brick' heating or radiation surface over the crucible, thereby giving more heat to the metal and securing greater rapidity in heating'. This results in'increased furnace capacity, greater fuel economy and longer lite of the furnace roof.- By a system of staggering' the checker-like brick, have reduced the rate of the drafty through these checkers which forces the draft ol' greatest velocity to occur at the extreme `or innermost end oif the brick. Therefore, the hottest point is at the end of the brick. In this manner l have in a sense created a thermal dai-n protecting that part of the brick sustaining' the arch. 'pressure or structural load. Furthermore by the reduction of the velocity of this draft, I have diminished the high abrasive action of the sharp )articles of coal dust and carbon which are rawn from the gas producers and blasted in an impinging llame against the roof, which is recognized as a destructive factor in open hearth operation. A reduction in the velocity of the draft will reduce the amount oi suspended slag particles and iron oxide in the Jfurnace, thereby reducing slugging action which is also highly destructive to the root` structure under present design and practice.l

I' have also devised an improved method of constructing the arch or 1furnace roof from the. brick of my invention. lt is of utmost importance that the suspended ends of these arch brick be free and clear of every particle of joint cement or material used in laying up an open 'hearth root in order that the endv and sides be permitted to expand freely. ln constructingI this arch, the brick are dipped. into thc joint cement material in the usual way, the checker end wiped clear and placed on the usual centers by ineansot any suitable forms ol' cardboard, rooiingi; paper, green Wood or the like, or the reduced ends may be protected against the cement `material lby a sheath or carton, such as is illustrated in Fig. 7 orn the drawing, the saine ybeing carefully placed around the checker lends.

rihc joint material or cement in the arch is retained .in position and not pcimitted to lill or seep between the checker ,ends of the brick. Dimensions are not of importance and l contemplater wide varia-- tions in dimensions :is experience may dictate.

.This inif'ention isl not confined in principle to the use ci silica material, but to any runner i.

refractory material, such as lire clay` magnesia, chronic, bauxite, flint clay, diasporc, spinal, rutile, carbon compounds, bonded tridyniite orany other refractory material and compound.

` The use ci' the terni brick in this description shall be broadly applied and shall include in its meaningi brick, sizes, tile, special shapes and cenicnts coinn'ion and usual to the rc'fractories business as now practiced, and the use of this term brick shall be thus broadly construed in determining; the scope ci this patent.

In embodyingy the invention in a furnace root of 13 inch construction l use silica brick or blocksot' four and one-half by four and one-halt' by thirteeninches, or four and one-halt by four by thirteen inches, or four and one-half by three by thirteen inches,

nine inches of the thirteen inch dimension being' of such construction as is usual in a square brick or key or wedge brick :is might be desired or necessary to use. At the nine inch point the lower end ol the brick Will be tapered for one-haii inch on all 'four sides to :i size Where the reduced end would he three and three quarter inches square by three and one-haii inches in length. It is within the scope of this invention `to vary the tapering point as described so as to make the dimension, if desired, a tapering line ot four inches and from four and onehalf to three and three quarter, inches.`

When set in the arch of the furnace roof the nine inch end of the briclrswill form the arch complete and the remaining four inches which is of reduced area, say three andvtli'rec quarter inches, will be independently suspended below the point at which the arch strain or pressure is bearing. These brick must be alternately staggered to break joints by commencing on one-half brick in alternate courses in a usual and ii'cll known Way. By the construction described tlie Velocity of the draft is reduced through these checkered ends. as hereinbefore stated.

@ne embodiment of the invention is illustrated in the accompanying drawing wherein Fig. l is a transverse Vertical sectional vieur of an open hearth furnace constructed izo as in the case of the remaining brick, illustrated; and 1 Fig. 7 is a sectional view of a brick sliowing a protecting shield used when the arch is in course of construction.

In the drawing 5 desifrnates Vthe buck stays, 6 the Crucible and :i ,which support the arch ory roof S. This arch or roof may be of any desired curvature and may be composed of varying sizes and sha )es of brick, it being distinctly understood t at the invention is not limited to any particular manner of assembly since it is manifest that this ina-y be varied at will and within the expected skill of those versed in this art.

It is only essential, to secure the advantages by reducing the cross sectional area of the -jlio portions of the brick.

brick at their inner ends to vformthe portions 10 which project below fthe body proper, of

the brick, and preferably connected there- .with by tapered shoulders 11.

y While I prefer to employ these tapered shoulders their use is not essential since the projecting -portions 10 may extend directly from the lower portions of the bodies of the brick, if desired. By providing these reduced projecting portions l0 and staggering thein in alternate courses as hereiiibefore described, I produce a roof of a checker work structure and while the flame as it sweeps along this checker work structureinayfind its way betweenA the various projections, as indicated by they arrows a in Fig. 2, it is manifesti; at the point of greatest velocity of the flanc will be below the ends offthe 'checker work structure and thus the many abrasive artic-les carried in the -blast of flame wil be caused to travel below the lower ends of the brick while a slower moving` body of heat will 'be more or less trapped in the spaces between the lower ends of the projections and the abutting' or contacting` It is this body of heat which forms the thermal dani previously Areferred to and acts in a measure as a protection to the actually contacting portions of the brick. The depending projections constituting the checker work of course become incai'ulescent and -thus hold a `vast amountJ of stored heat which is directed down upon the metal in the Crucible. Steel manufacturers and users of refractories in general are everywhere crying for better refractories and higher heat. `It must be admitted that there is some room for ini-' proyeineiit iu the refractories field but the tactremains that in most practices'of the industry involving the use of high heat the working teiuperatiirc conditions of furnaces are close to the limit of the refractories to the side walls' withstand without fusing.' It is a visionary idea to think of securing refractoryv materials which will withstand temperatures' much in excess of those already employed. Higher heat is not the panacea for the diiticulty but rather more heat, more radiation, more heat of the saine temperature and mre scientific furnace construction. It is manifest that the present invention admirably secures this result by providing` a structure which' will (a) Greatly increase the heating and radiating surface,

(b) Slow up the draft in the channels between the checker work enough to give the heat supplied Aample time to do its work before it finds its way to the discharge iues and,

(c) Incorporate this idea in a structureA wherein the very features that are employed to secure this increased heating and radiating' surface ai'e also made to protect the Afurnace roof against the ordinarily destructive effect of expansion.

It is to he understood that the invention is not limited to the precise 4construction set forth but that it includes within its pur`A view whatever changes fairly7 come within either the terms or the spirit of the appended claims.

Having described my invention what I claim-is:

l. A furnace roof of vrefractory materia of staggered checker work construction.

2. A furnace roof of refractory brick having reduced inner ends which lie in spaced and staggered relation to each other and which project inwardly beyond the contacting portions of the brick.

3. A furnace roof of refractory brick having reduced inner ends which project inwardly beyond kthe body portions of the brick, said bricks being laid up in stag *gered formation to'cause said reduced ente lzd checker work construction wherein the con-. tacting )ortions of the bricks at the intrados line oft e arch are materially above the ends of said brick as and for the purposes set forth.

5. A top for an open hearth furnace of the character wherein the draft. is longitudinally of the furnace comprising a plurality of refractory bricks laid up as a selfysupporting arch and wherein the extreme heatedinner ends ofthe brick in said roof lOl) iet

aff:

are free-fo expand being relieved of the structural or arch strain and said .ends also protecting the intrados line of the roof arch against the maximum heat temperature.

(3. In a metalllugical furnace of the characier wherein the draft is longitudinal of the furnace, a furnace roof of checker constructionnthe elements of whichproject inwardlv beyond the intr-ados hne 'of the roof, said checker construction serving to increase the radiation area and reducing the draft velocity vabove the inner 'ends of sadelements.'

T. fr furnace of the type wherein the draft is'=longitudinal1y of he furnace and means associated with the furnace roof for creating a thermal dem thereunder, said moana.

comprising a checkervsfork construction be; .ueath which the draft of greatest velocity flows, l y 8., In an open hearth furnace ofthe charremera refractsa'y 'brichsdaid up as a self-support ing arch in which the intrados line of the arch has been raised above the heated end of the brick composing said arch.

l0. The'nie'hod of constructing a furnace of bricks whichA consiste of enclosing the inner ends of said 'bricks in a shield tg pro tect Ithem while being laid in place.

. In testimony whereof I hereunto yaffix my.

signature.

creanme arene oran/Fono. i 

